Throughout the 1970s and 1980s, news headlines were splashed with serial murder cases such as the Green River Killer, Ted Bundy, John Wayne Gacy Jr, Richard "Night Stalker" Ramirez, the Zodiac Killer, and BTK. The FBI notes that this sparked a massive "renewed public interest" in serial killers – a similar curiosity of which had previously sprung up in the 19th century following the notorious murders of “Jack the Ripper” in Victorian London.

Now, it’s the post-Making A Murderer Internet age, when it has never been easier to indulge in your morbid curiosity. With this, too, comes a whole new bag of serial killer-infused Netflix documentaries, TV series, podcasts, Reddit threads, movies, and even the odd IFLScience article.

As much as we might be repulsed by the actions of serial killers in theory, it seems we can’t get enough of them. So what is it about these characters that capture the human imagination so strongly?

For many, it’s no different to the buzz you get from watching horror movies. Each stab, scream, or stalkery look comes with a rush of neurotransmitters and a physiological change in the body, such as an increased heart rate, increased breathing rate, and increased blood glucose levels – the same reaction we get with excitement. It also administers a dose of a dopamine into your brain, the neurotransmitter famously associated with pleasure, mainly food and sex, but also during times of fear.

We get this shot of feel-good chemicals because it's often helpful for our survival. If we are simply spectating the threat from a cool distance, however, then the neurotransmitters are there but in a very different context. It's effectively a safe place for us to relish in a binge of dopamine and adrenaline.

“I would offer that we learn about serial killers through the media – documentaries, books, online sources, and films – and that these are safe ways to explore such a morbid topic,” Bridget Rubenking, assistant professor at the University of Central Florida and media psychology scholar, told IFLScience. “Exploring all the negative things – ranging from fearful or frightful, to quite depressing and melancholy – is common and quite easy to do through media, where the risks are substantially less than exploring these subjects in non-mediated environments.”

Rubeking’s 2014 study looked into how we react to films and TV shows that tickle our sense of disgust and revulsion. Her team measured the physiological changes of participants as they watched videos that portrayed three different types of disgust: death, gore, and socio-moral disgust, like cheating and betrayal. When it came to death and gore, the initial reaction was negative, but it also provoked the strongest physiological indication of “arousal” and “attention”.

It’s easy to think that human behavior is simply guided by a desire to pursue pleasure, avoid pain, and survive. Yet paradoxically, we’re attracted by the repulsive. It’s the same reason why you rubberneck at car crashes, search for graphic videos on LiveLeak, or enjoy watching a celebrity meltdown on Twitter.

So far, though, this could all apply to any old gruesome stuff. Why serial killers in particular?

For starters, there is something appealing and definitely freeing about being unconstrained by conventional morality. Serial killers are particularly good at this. They rarely commit their murders via conventional reasoning like revenge, jealousy, or fear. Instead, the FBI say that “regardless of the motive, serial murderers commit their crimes because they want to.“

As fascinating as it might be to be "moraless", it’s certainly something we want to avoid.

“If you strip down all animals, our motivational systems are comprised of two systems,” Rubenking added. “First, an appetitive, or approach system, which leads us to seek out opportunities that aid self and species survival. Namely, food and sex. The other nested system in the motivational system is the aversive or defensive system. It is what ramps up when we’re faced with threats and guides protective actions.”

“From this perspective, learning what is disgusting is functional. Disgust is often conceptualized as originating in our oral rejection system: Basically, a 'don’t eat that, it’s gross, you’ll die' response. It has, over time, been co-opted to tell us also what not to have sex with, and later on, what people and practices to avoid.”

However, this macabre interest in the topic far exceeds its scope. Realistically, the chances of getting nabbed by a serial killer are very, very slim. The curiosity might not be straightforward in its practicality, like learning to avoid foul-smelling meat, but it's a testament to our ability as super-brained mammals to toy around with abstract concepts like good, evil, and death.

It seems that being fascinated with death, and the most theatrical purveyors of death, is something that makes us human.